The present invention relates to a metal solution used as a raw material for forming a nickel metal thin film directly on a substrate and to a method of forming a nickel metal thin film using the said metal solution.
A nickel metal thin film is formed in general by, for example, an electroplating method, a chemical plating method, a printing method or a vapor deposition method.
The most general process of synthesizing a nickel metal film is an electrolytic process. In the case of employing the electrolytic process, however, the coating substrate is limited to a conductive substrate. On the other hand, an electroless plating makes it possible to apply coating of a metal film to an insulating substrate. However, it is difficult to control the thickness of the coated film. In addition, since hypophosphorous acid is used as a raw material, the resultant nickel metal film is caused to contain phosphorus as an impurity.
It is also possible to utilize a screen printing method using a metal paste containing a metal powder as a main component. In this case, however, it is difficult to use a fine nickel metal powder.
Further, it is known that in this process a nickel oxide film is formed first, followed by reducing the nickel oxide film with hydrogen so as to convert the oxide film into a nickel metal film. However, a reducing atmosphere is utilized in this method, which provides a serious obstacle in terms of the film forming cost and the film forming process. In addition, the nickel film thus formed is porous.
An object of the present invention is to provide a solution for forming a nickel metal thin film, which is used as a raw material solution for forming a high purity nickel metal thin film directly on a substrate by a simple process.
Another object of the present invention is to provide a method of forming a high purity nickel metal thin film directly on a substrate by a simple process and with a low cost.
According to a first aspect of the present invention, there is provided a solution for forming a nickel metal thin film, the solution being formed of an alcohol solution containing nickel ions and a reducible chelate type ligand having a hydrazone unit.
According to a second aspect of the present invention, there is provided a method of forming a nickel metal thin film, comprising the steps of:
coating a substrate with a solution for forming a nickel metal thin film, the solution being formed of an alcohol solution containing nickel ions and a reducible chelate type ligand having a hydrazone unit so as to form a gel film; and
subjecting the resultant gel film to a heat treatment under an inert gas atmosphere.
Further, according to a third aspect of the present invention, there is provided a method of forming a nickel metal thin film, comprising the steps of:
coating a substrate with a solution for forming a nickel metal thin film, the solution being formed of an alcohol solution containing a reducible chelate type ligand having a hydrazone unit and nickel ions, the reducible chelate type ligand being contained in an amount two times as much in the molar amount as the nickel ions, so as to form a gel film; and
subjecting the resultant gel film to a heat treatment under an inert gas atmosphere.
In the solution of the present invention for forming a nickel metal thin film, it is desirable for the reducible ligand to be contained in an amount two times as much in the molar amount as the nickel ions.
In the method of the present invention for forming a nickel metal thin film, the substrate can be coated with the solution for forming the nickel metal thin film by means of a dip coating method or a spin coating method.
Also, it is desirable for the heat treatment to be carried out at temperatures not lower than 400xc2x0 C. for 10 to 30 minutes.
Further, an insulating substrate can be used as the substrate on which the nickel metal thin film is formed.
Additional objects and advantages of the invention are given in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.